to locate the game files you have to go to :
"C:\Program Files (x86)\Steam\steamapps\common\Left 4 Dead 2\left4dead2\cfg"

after entering the folder you'll find file named "addonconfig.cfg"


Note : If you didn't see the file type .cfg, its okay just make sure the file name is "addonconfig"

.
if you wanna show files extensions in any folder you're in at the top click view and mark "file name extensions, as shown in screenshot :

Now to the most important part editing the file.
1- Right click on the file "addonconfig.cfg" and choose open with as shown .



2- Then choose notepad or any text editor you have installed in your pc, notepad is fine.


3- Now head down until you find "RestrictAddons".





As you can see here :
{
"default" "1"
"versus" "1"
"scavenge" "1"
"mutation15" "0" // versus survival
}

0 = False
1 = True

Like This :


{
"default" "0"
"versus" "0"
"scavenge" "0"
"mutation15" "0" // versus survival
}

Feel free to copy them.

NOTE:

This method only works in local servers and single player.

As you you can see this also applies to "scavenge" "mutation15", and other mods.
If you want me to make a guide about the other mods and their "id", let me know.

Please if you find the guide helpful favorite + reward, for more guides.



Left 4 Dead 2 - Addons - Versus - Mutation - Versus Player - Versus Mods - Versus Not Working - Addons Versus - Versus Addons - Add-ons - Fix - Change - Edit - Make - Config.